Method for assembling a blade of a wind turbine

ABSTRACT

The wind turbine has a tower; a nacelle; and a hub comprising a hub connection flange for being detachably connected to a blade connection flange of a rotor blade. The method comprises the next steps: fixing a first positioning element in the nacelle or in the top of the tower; fixing a second positioning element to the blade in a root blade area; lifting the blade to the vicinity of the hub connection flange by means of lifting means; putting into contact the first and the second positioning elements; providing an accurate position of the blade connection flange, prior to the connection to the hub connection flange, by cooperation of the first and second positioning elements; and providing, when the first and the second positioning elements cooperate, a trajectory of the blade which is parallel to the axis of a hub connection hole, disposed in the hub connection flange, the provision of the trajectory being carried out by means of a guided element joined to either the first positioning element, the second positioning element, or both.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of application Ser. No.13/909,886, filed Jun. 4, 2013, now U.S. Pat. No. 9,446,446, whichapplication claims priority from U.S. Provisional Patent Application No.61/655,311, filed on Jun. 4, 2012, both of which are incorporated hereinby reference.

BACKGROUND

Currently, there is a trend in the wind energy sector toward higherpower rating of wind turbines in order to reduce the cost of energy.This causes a subsequent increase in weight and dimensions of most ofthe components comprised in the wind turbine, including the rotor.Another trend for increasing energy capture has been to design tallertowers to take advantage of greater wind energy at higher levels aboveground, most of the designs nowadays being 100 m high and taller.

Particularly relevant for the assembly and maintenance costs are towerheight, rotor diameter and weight of hub and blades, due to their directimpact on crane capacity and cost of the same, being the most importantthe first of them. Tower height determines the system and processrequired for assembling components relatively heavy and/or bulky, suchas the hub or the blades: an increase in height implies bigger bendingmoments that have to be stood by the cranes, and that make necessary theuse of higher capacity cranes than the actual weight being lifted andwhose use can be really expensive.

In the specific case of operations for assembling blades, there arethree procedures most commonly used:

Preassembling the hub and the blades at ground level and lifting thepreassembled system to the top of the nacelle;

Lifting and assembling each blade one by one in a horizontal positionand connecting them to the hub on top of the tower. In order to lift theblade in such a position and avoid it from turning and collapsing, thisprocess requires either two cranes connected to the blade in both sidesof it, or a single crane making use of a special tool to compensatepossible variations of the center of gravity of the blade in relation tothe position of the lifting point; and

Lifting and assembling each blade one by one in a vertical position andconnecting them to the hub on top of the tower. It usually comprises ahoisting system and a plurality of pulleys installed within the hub andnacelle, in order to avoid the use of a big crane.

Among the last of the listed procedures there are several alternativesin the state of the art:

US Patent Application Publication US 2009/0058096 (Wobben) discloses amethod of mounting or dismantling a rotor blade of a wind powerinstallation without using a crane. A cable is stretched between a partin the outside surface of the hub of the wind power installation and thebottom region of the wind power installation. The rotor blade is movedalong the cable upwardly upon mounting or downwardly upon dismountingthe blade.

U.S. Pat. No. 8,083,212B2 discloses a method of mounting a rotor blade,which allows the blade to be mounted and removed without using multipleconstruction machines. The suspension device has a pulley inside thehub, a holding section inside or outside a blade, and a winch. Thepulley leads a suspension wire from the rotor hub, on which the blade isto be mounted, to the holding section fixed at the root end and insidethe blade. The holding section holds the mounting end side of the bladesuch that a line connecting the center of gravity of the blade and aconnection section to which the suspension wire is connected intersectswith the longitudinal axis of the blade. The winch is placed on theground and raises and lowers the holding section/blade by pulling in andpaying out the suspension rope.

WO2011064659A2 discloses a system for assembling a rotor bladecomprising a modular truss system including at least one pulley and twomounting beams, each mounting beam being detachably connected to a hubconnection flange, thereby positioning the pulley beam above a furtherhub connection flange and a blade pulley system including at least onepulley and being detachably connected to the blade connector portion ofa rotor blade. To avoid any damage to the hub connection flange or thepitch bearing, they are aligned before they come in contact with eachother by mean of a plurality of flexible cables, each of them connectedto the outer race of the pitch bearing of the blade being assembled,passing through holes in the respective flange of the hub and furtherconnected to a hoist arranged in the hub or the nacelle.

The above-described publications have the disadvantage of comprisingelements of the lifting system (i.e. pulleys, winches, cables, etc.)inside the hub and, therefore, their position for mounting one blade isnot proper for the assembly of another one: these elements have to beadequately mounted once per blade assembled; that is thrice for aconventional rotor. This operation is time consuming and increments thecost of the whole method. Moreover, those elements have to bedisassembled and lowered to the ground once the operation has finished,and so, they have to be moved to an access door provided in the rear ofthe nacelle or in the front of the hub.

Moreover and even more important, they do not provide an efficient androbust system for positioning and guiding the blade into engagement withthe hub connection flange, this operation being crucial for preventingdamage from being infringed to any element.

SUMMARY

It is desirable to provide an apparatus and method, which facilitatesthe repair and replacement of wind turbine blades, minimizing the numberof steps and the time required, not only for the assemble/disassembly ofa single blade, but also of a whole rotor and, therefore, reduces thecosts of such repair and replacement.

In order to provide a solution to the above mentioned drawbacks ofstate-of-the-art systems and methods, a system and a method forassembling and disassembling components from a wind power turbine aredisclosed herein.

The wind turbine comprises a tower resting on a base, a rotor comprisingat least one rotor blade having a blade connection flange and a nacellemounted atop the tower. The rotor further comprises a hub rotatablyconnected to a nacelle and comprising a plurality of hub connectionflanges adapted to be detachably connected to a blade connection flangeof a rotor blade.

The system for assembling and disassembling components from a wind powerturbine further comprises: at least one first positioning elementadapted to be attached to a nacelle or to a tower in a top area andconfigured to provide an accurate position of the blade connectionflange prior to connection to a hub flange, i.e. of the bolts of theblade with respective holes in the hub flange. For this purpose, it isconfigured to cooperate with a corresponding second positioning elementadapted to be joined to the blade in a root blade area. In this way, anadequate position of the blade connection flange with respect to the hubconnection flange can be ensured even by lifting the blade from a pointfixed to a non-rotating component located at the top of a tower, bynon-rotating meaning that it does not turn as the rotor turns, as forexample, to a nacelle or tower. Therefore, it provides the advantageover the state-of-the-art methods of raising the blade form anon-rotating point while ensuring an accurate position of the blade withrespect to the hub, thus avoiding the inclusion of system elements likepulleys and cables inside the hub, which have to be changed once perblade being mounted.

In an embodiment, the system of the invention further comprises oneguiding element configured to provide an adequate trajectory of thesecond positioning element in the final movement of the blade towardsthe hub and when the first and second positioning elements cooperate. Byadequate trajectory, an upward trajectory of the blade substantiallyparallel to the axis of a hub hole is meant. The guiding element isjoined to either the first positioning element, or the secondpositioning element, or both. In an embodiment, it is configured tocooperate with a corresponding second guiding element attached to theblade.

The guiding element provides a further advantage of the proposed systemover the state-of-the-art that is adjusting the trajectory of the bladein its final movement so as to ensure that, if the angle of the blade isadequate, i.e. if the bolts of a blade are parallel to the holes inwhich they are to be inserted, and given that the position is precise,the insertion of the bolts will be performed with no interference of thebolts with the hub flange or any other components. The angle of theblade can be modified by a retaining cable connected to the blade and toa retaining crane, for example.

Supporting means adapted to be joined to the blade in a supporting bladearea located between a maximum chord area and the blade tip for a betteradjustment of the angle of the blade in its final movement toward thehub and prior to inserting the blade stud or bolts into respective hubholes. The supporting means are adapted to rest on the tower or on atleast one tensioned cable connected between the ground area and thenacelle or tower. They provide an adequate alignment between the hubconnection flange and the blade connection flange, by separating thesupporting blade area from the tower at a distance that, when the firstand second positioning elements cooperate, the axis of a blade stud issubstantially parallel to the axis of a hub connection hole.

With the proposed system, a reduced number of operations are requiredfor assembling a complete rotor with respect to previous methods, byhaving the elements required for the operation fixed to a non-rotatingcomponent of the wind turbine, and a precise movement and positioning isensured.

From now on, details of specific embodiments of the invention aredisclosed with reference to the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side general view of a system for assembling a blade to ahub.

FIG. 2 is a front general view of a system for assembling a blade to ahub.

FIG. 3 shows a side view of a nacelle comprising two first positioningand guiding elements and two pulleys.

FIG. 4 shows a top view of a nacelle comprising two first positioningand guiding elements and two pulleys.

FIG. 5 shows a detail of the system for assembling a blade (stage 1 of asequence of 4 stages: second positioning and guiding element approachingthe first positioning and guiding element).

FIG. 6 shows a detail of the system for assembling a blade (stage 2 of asequence of 4 stages.

FIG. 7 shows a detail of the system for assembling a blade (stage 3 of asequence of 4 stages).

FIG. 8 shows a detail of the system for assembling a blade (stage 4 of asequence of 4 stages).

FIG. 9 is a side view of a blade raising tool used in a preferredembodiment.

FIG. 10 is a top view of a blade raising tool used in a preferredembodiment.

FIG. 11 is a section A-A′ of FIG. 10.

FIG. 12 shows a side view of a wind turbine comprising a system asdescribed in the specification plus a blade raising tool comprisingwheels resting on the tower surface.

FIG. 13 shows a front view of a wind turbine comprising a system asdescribed in the specification plus a blade raising tool comprisingwheels resting on the tower surface.

FIG. 14 shows a side view of a wind turbine comprising a system asdescribed in the specification in which the first guiding elementcomprises a couple of tensioned cables attached on a first end to theregion of the nacelle, and on the second end, to an attaching pointprovided at the ground level.

FIG. 15 shows a front view of a wind turbine comprising a system asdescribed in the specification in which the first guiding elementcomprises a couple of tensioned cables attached on a first end to theregion of the nacelle, and on the second end, to an attaching pointprovided at the ground level.

FIG. 16 is a section B-B′ of FIG. 14.

FIG. 17 shows a detail of the system for assembling a blade wherein aguiding element is joined to the second positioning element and when theblade is approaching the first positioning element.

FIG. 18 shows a detail of the system of FIG. 17 wherein the guidingelement is joined to the second positioning element and when the secondpositioning element comes into contact with the first positioningelement.

FIG. 19 shows a detail of the system for assembling a blade wherein aguiding element is joined to both the first and the second positioningelements and when the blade is approaching the first positioningelement.

FIG. 20 shows a detail of the system of FIG. 19 wherein the guidingelement is joined to the first and the second positioning elements andwhen the second positioning element comes into contact with the firstpositioning element.

DETAILED DESCRIPTION

Referring to the drawings the system for assembling and disassemblingcomponents from a wind power turbine comprises:

One first positioning element (1) adapted to be attached to a nacelle(2) or to a tower in a top area and configured to provide an accurateposition of the blade connection flange (3) prior to connection to a hubflange (4), i.e. of the bolts (5) of the blade (6) with respective holes(7) in the hub flange (4). For this purpose, it is configured tocooperate with a corresponding second positioning element (8) fixed tothe blade (6) as shown in FIGS. 9-11. Preferably, the system comprisestwo first positioning elements (1) located in the nacelle (2), attachedin the front part of the main frame (9), one in each side of the mainshaft (10) shown in FIGS. 3 and 4 and configured to cooperate with twosecond positioning elements (8) fixed to the blade (6), so as to providean accurate position of the blade flange (3) with respect to the hub(11). Optionally, the first positioning elements (1) are fixed to themain frame (9) in such a way that their position in relation to the mainframe (9) can be controllably modified when the second positioningelement (8) is correctly placed in relation to it, for example, bymoving them in any of the three coordinate directions by means of linearactuators, driving means, screws or the like;

One guiding element (12) located in the region of the nacelle (2) andconfigured to provide an adequate trajectory of the second positioningelement (8) in the final movement of the blade (6) towards the hub (11).By adequate trajectory, an upward trajectory of the blade substantiallyparallel to the axis of a hub hole is meant. For this purpose, in someembodiments it is configured to cooperate with a corresponding secondguiding element (8) attached to the blade (6).

For a better adjustment of the angle of the blade (6) in its finalmovement toward the hub (11) and prior to inserting the blade stud orbolts (5) into respective hub holes (7), the system also comprises somesupporting means (13) adapted to be joined to the blade (6) in at leastone supporting blade area located between a maximum chord area and theblade tip. Another supporting means are provided in a blade raising tool(as can be seen in FIG. 12). The supporting means (13) are adapted torest on the tower (14) or on at least one tensioned cable (36) connectedbetween the ground area and the nacelle (2) or tower (14). They providean adequate alignment between the hub connection flange (4) and theblade connection flange (3), by separating the supporting blade areafrom the tower (14) at a distance that, when the first (1) and second(8) positioning elements cooperate, the axis of a blade stud or bolts(5) is substantially parallel to the axis of a hub connection hole (7).

The system for assembling and disassembling components from a wind powerturbine further comprises some lifting means including the followingelements:

A pulley system including at least one pulley (15) detachably connectedto the main frame (9) of the wind turbine. It (15) can also be connectedto any other component stationary connected with the main frame (9) ortower (14). Said connection may be done via beams or any otherstructural component in order to achieve an optimal location of thepulleys (15) with respect to the hub (11).

Preferably, the pulley system comprises two pulleys (15) in the frontpart of the main frame (9), one in each side of the nacelle (2) as shownin FIGS. 3 and 4. The pulley system guides at least one cable (16) froma blade raising tool (17) wherein the second positioning element isdisposed, to a hoisting system (18) as shown in FIG. 1.

At least one cable (16) connected to a blade raising tool (17) in oneside and to a hoisting device (18) in the other side through one pulley(15) provided in the nacelle (2). In a preferred embodiment there aretwo cables (16) connected to the blade raising tool (17) and to twohoisting devices (18) located on the ground in the proximity of thetower (14) base, through two pulleys (15) located inside the nacelle(2).

To lower or raise a rotor blade (6), the system comprises some kind of ahoisting device (18). Such hoisting device (18) may be arranged on theground, for example on a truck, or may be an integral part of the windturbine, arranged e.g. in the nacelle (2) or the tower (14). In theshown embodiment, the hoisting device (18), in form of a winch, islocated on the ground outside the turbine. The winch is a mechanicaldevice that is used to wind up or wind out the cable (16) to pull thecable (16) in to raise the blade (6) or let the cable (16) out to lowerthe blade (6). In a preferred embodiment there are two winches connectedto two cables (16) located on the ground in the proximity of the tower(14) base.

This embodiment provides a degree of redundancy to avoid fatal damage ofthe blade (6) in case there is a failure of the system, for example, ofone of the two winches.

The elements of the system are attached to the blade (6) and main frame(9) only if a blade (6) should be mounted or lowered, and therefore noadditional weight is added to the turbine in its operating condition.

Preferably, the blade raising tool (17) is attached to the blade (6) onthe outer surface. One possibility for said attachment is to fixate thetool (17) via bolts (34) to t-bolts (35) embedded in the blade (6) inthe area of the root. They have to be accessible for extraction once theblade (6) is connected to the hub (11) in order to descend the tool (17)and proceed to the connection of another blade (6). For this purpose, ina preferred embodiment some thru holes are provided in the t-bolts asshown in FIGS. 9-11.

FIGS. 5-8 show four different stages in the process of assembling ablade (6).

In FIG. 5 a detail of the system for assembling a blade (6) is shown.Attached to a main frame (9) of the wind turbine, one of the pulleys(15) and one of the first positioning (1) elements and one of the firstguiding (12) elements are shown (the others being in the other side ofthe shaft (10)). A cable (16) is passed through the pulley (15) andconnected to the blade raising tool (17) in one of its ends and to awinch (not shown) in the other one. In this specific embodiment, thecable (16) also passes through a first thru hole (19) provided in thefirst positioning element (1).

The blade raising tool (17) is attached to the blade (6) via bolts (34)connected to the T-bolts (35) in the area of the root. It comprises apair of second positioning elements (8), as shown in FIGS. 9-11. A pairof cables (16) is connected to the blade raising tool (17), in thisspecific embodiment being connected directly to the second positioningelements (8), more precisely, to the upper end of them. This is anon-required feature, but it can be advantageous, for example, forattaching the blade raising tool (17) to the blade (6) when the blade isalready assembled.

The blade connection flange (3) of the blade (6) is provided with bolts(5) protruding through it and configured to be connected to a bladepitch bearing (20) attached to the hub (11), by inserting said bolts (5)into respective holes (7).

The first positioning element (1) is provided with a second hole (21)larger than the upper end of the second positioning element (8) (beingfor example hemispheric or conical-shaped) and configured to allocatesaid second positioning element (8) in a specific position. The firstpositioning element (1) is also connected to a first guiding element(12) in a movable manner, in such a way that it can be moved upwards anddownwards and parallel to the holes (7) provided in the blade pitchbearing (20).

Also important is the fact that the first (1) and the second (8)positioning elements are attached to the main frame (9) and to the blade(6) respectively, in such a position that they come into contact beforethe upper end of the bolts (5) of the blade (6) reach the level of a hubcover (22). This provides the possibility of adjusting the position ofany of those elements prior to interference and potential damage of thebolts (5) or the hub cover (22) or any other element herein.

In the second stage, the second positioning element (8) is adequatelycentered with respect to the first positioning element (1), the shape ofeach of them enabling this as the blade (6) is moved upwards by means ofthe cable (16) and the winch. In the case shown in the FIG. 6, thesecond positioning element (8) comprises a spherical end (24) thatslides in contact with the second hole (21) of the first positioningelement (1).

Preferably at this point but mandatory at stage three, the bolts (5) ofthe blade have to be parallel to the holes provided in the hub for theirinsertion. This cannot be done by leaving the blade in a verticalposition: generally, the bolts are protruding from the blade connectionflange in 90°, the blade connection flange being perpendicular to theaxis of a blade, and the angle formed by the blade axis and an imaginaryvertical plane has to be kept equal to the sum of the tilt angle, plusthe conning angle and the preconning angle, i.e. the angle that isideally formed between a blade axis and the vertical plane when theblade is finally assembled (being the tilt angle the angle formed by theshaft axis and a horizontal plane; the conning angle, the one comprisedbetween a blade axis of rotation and a plane perpendicular to the shaftaxis; and the preconning angle, the angle formed between the blade axisof rotation and a blade axis.

To do this, a retaining cable (23) attached to a retaining crane (notshown) can be used as shown in FIG. 1. In another embodiment shown inFIGS. 12 and 13, the desired angle of the blade (6) is set by adequatedimensions of at least a couple of supporting elements (13) attached tothe blade raising tool (17) and resting on the tower (14) surface. Thosesupporting elements (13) may comprise some sort of wheels (29) in theirend contacting the tower (14) surface, so as to roll on it as the blade(6) is raised. In still another embodiment, the desired angle of theblade (6) is set by adapting the position of an attaching point on theground of a couple of guiding cables (36) acting as a first positioningelements, as shown in FIGS. 14 and 15.

In stage 3 shown in FIG. 7, the first positioning element (1) is movedupwardly guided by the first guiding element (12) as the blade (6) israised, and, therefore, the trajectory of the second positioning element(8) remains parallel to the holes (7) of the pitch bearing (20). Thefirst guiding element (1) can either be moved upwards directly beingpushed by the second positioning element (8), or by actuating on itthrough, for example, some bolts.

At this moment (prior to inserting the bolts (5) of the blade (6) intorespective holes (7) located in the pitch bearing (20)), if said bladeconnection bolts (6) are not properly positioned in relation to theholes (7), an accurate correction can be done by adjusting the positionof the first positioning (1) and guiding (12) elements attached to themain frame (9). Obviously, coordination is required when adjusting theposition in the case of having one positioning element (1) in each sideof the shaft (10) (the same occurring with the cables (16) and theactuation of the winches when raising the blades (6)). Optionally,cables (16) can be attached to a same shaft of a winch.

Once the bolts (5) are adequately positioned, the raising movement ofthe blade (6) is done in the direction set by the guiding element (12),i.e. the desired angle of the blade (6), with the blade positioned in anadequate angle, the bolts of the blade being parallel to the holes (7)of the hub. And, finally, as shown in FIG. 8, the bolts (5) of the blade(6) are inserted in respective holes (7) and the connection of them canbe finished, for example, by connecting nuts to their ends.

FIGS. 9-11 show an embodiment of the blade raising tool (17) (the rootpart of a blade raising tool in one embodiment). As it can be seen it isattached to the blade (6) on the outer surface and fixated via bolts(34) to the t-bolts (35) embedded in the blade (6) in the area of theroot. They have to be accessible for extraction once the blade (6) isconnected to the hub (11) in order to descend the tool (17) and proceedto the connection of another blade. For this purpose, in a preferredembodiment some thru holes are provided in the t-bolts (35).

The cables (16) used for raising the blade (6) are attached on theirsecond end to the blade raising tool (17).

In a preferred embodiment the blade raising tool (17) comprises twohalves (27) rotatably connected through a hinge (25). This feature makeseasier the operations of attaching and detaching the raising tool (17).A security attachment element (26) for closing and joining together thehalves (27) is also provided in form of a hydraulic piston, for example.

A couple of second positioning elements (8) are provided on two sides ofthe blade raising tool (17), configured to cooperate with the firstpositioning elements (1) attached to the main frame (9) or tower (14).

The way in which the blade raising tool is attached to the blade, moreprecisely, the position of the same is next described. As the bladeraising tool (17) comprises second positioning elements (8) that wouldaffect the position of the bolts (5) with respect to associated holes(7) comprised in the hub (11), or the pitch bearing (20), the positionof those elements (8) with respect to the bolts (5) prior to any raisingoperation has to be accurate.

Also, in a preferred embodiment, when performing theassembly/disassembly of a blade (6), the hub (11) is oriented upwind andthe blade (6) is raised in a feathered position in order to minimize thethrust caused by wind and ensure a secure operation. The pitch bearing(20) is also positioned in a feathered position, and it must be ensuredthat each bolt (5) enters its respective hole (7) (an error of onerotated position has a really negative impact on production and loads).A bolt indicating the zero position is to be inserted in the zeroposition hole of the blade pitch bearing (20).

For this purpose, the orientation of the blade raising tool (17) withrespect to the bolts (5) of the blade (6) is controlled by fitting abolt (34) in associated T-bolt (35). For ease of this kind ofoperations, colored bolts, holes and parts of the blade raising tool(17) can be provided.

The system further comprises supporting means (13) adapted to be joinedto the blade (6) in a supporting blade area located between a maximumchord area and the blade tip; being the supporting means adapted to reston the tower (14) or on at least one tensioned cable and to separate thesupporting blade area from the tower (14) at a distance that, when thefirst (1) and second (8) positioning elements cooperate, the axis of theblade stud is substantially parallel to the axis of the hub connectionhole

In another embodiment, the blade raising tool (17) comprises asupporting-part configured to be located in a supporting blade arealocated between a maximum chord area and the blade tip, for example, theregion of the center of gravity and attached to a root part so as to bemoved upwards as the root part is pulled by the cables (16) and beingthe root part configured as explained before. This supporting-partcomprises some kind of adjustable elastic cradles configured to fit theblade profile shape in the supporting blade area in order to transmitpart of the weight loads of the blade (6) either to a tower (14) or to acouple of guiding cables (36) acting as a first positioning elements,without damaging the blade surface. For this purpose, the supportingpart comprises some supporting means adapted to rest on the tower or onat least one tensioned cable and to separate the supporting blade areafrom the tower at a distance that, when the first and second positioningelement cooperate, the axis of the blade bolt is substantially parallelto the axis of the hub connection hole.

FIGS. 12-15 show two embodiments wherein the blade raising tool (17)comprises a center-of-gravity-part attached to a root part (31) asexplained before.

In the embodiment shown in FIGS. 12 and 13 a couple of supportingelements (13) are connected to the blade raising tool (17) in thesupporting-part (30) and resting on the tower (14) surface. Thosesupporting elements (13) may comprise some sort of wheels (29) in theirend contacting the tower (14) surface, so as to roll on it as the blade(6) is raised. Their length is set to be adequate to both the dimensionsof the tower (14) and the nacelle (2) in such a manner that, when thebolts (5) in the blade root are about to be inserted into respectiveholes (7), the desired angle of the blade (6) is ensured and the secondpositioning element (8) fits its position within the first positioningelement (1). In an embodiment, those supporting elements (13) comprisesome sort of actuators, as for example, electric or hydraulic piston, inorder to vary their length and adjust the blade angle.

In an embodiment, also a supporting element (13) provided with wheels(29) is connected to the blade raising tool (17) in the root part (31)in order to achieve an enhanced stability of the blade when beinglifted.

In the embodiment shown in FIGS. 14 and 15, the first guiding elementsserve also as first positioning elements and are a couple of tensionedguiding cables (36) attached to the main frame (9), their attachmentpoint position in the main frame being adjustable so as to provideaccurate position of the bolts of the blade with respect to the holes.The guiding cables are also connected to an attachment point (28)provided on the ground. Their angle is set by adjusting the position ofsaid attachment points (28) on the ground. In said embodiment, the bladeraising tool (17) also comprises a supporting-part (30) and a root part(31) that slide resting on the guiding cables. For that purpose, both ofthem (30, 31) are provided with second guiding elements (32) configuredto cooperate with the cables (36) acting as first guiding elements.Those second guiding elements actuate as well as second positioningelements.

The position of the attachment points (28) on the ground is adapted insuch a manner that, when the bolts (5) in the blade root are about to beinserted into respective holes (7), the desired angle of the blade (6)is ensured. As said before, those cables (36) acting as first guidingelements are attached to the main frame (9) (or other stationary part asfor example the tower (14)) to an attachment point which position may beadjusted so as to guarantee coincidence of the bolts with the holes (7).

When the blade (6) is finally connected to the hub flange (4) by meansof the pitch bearing (20), the system is dismantled using conventionaltools frequently used for that purpose within the state-of-the-art, likea hoist. For descending the blade raising tool (17), the cables (16)used for raising the blade (6) are used.

In a preferred embodiment, the nacelle cover (33) is suited with aservice door in the lower part of it in the region where the elements ofthe system are located.

A method for assembling and disassembling a blade with such a system isalso within the scope of this invention.

What is claimed is:
 1. A method for assembling a blade of a windturbine, the wind turbine comprising a tower having a tower surface andresting on a base, a nacelle mounted atop the tower, a hub rotatablyattached to the nacelle, the hub comprising a hub connection flangeadapted to be detachably connected to a blade connection flange of arotor blade, the method comprising the next steps: fixing a firstpositioning element in the nacelle or in the top of the tower, fixing asecond positioning element to the blade in a root blade area, liftingthe blade to the vicinity of the hub connection flange by means of alifting means, putting into contact the first and the second positioningelements; providing an accurate position of the blade connection flange,prior to the connection to the hub connection flange, by cooperation ofthe first and the second positioning elements; and providing, when thefirst and the second positioning elements cooperate by coming intodirect contact with each other, a trajectory of the blade which isparallel to an axis of at least one hub connection hole, disposed in thehub connection flange, the provision of the trajectory being carried outby means of a guiding element joined to either the first positioningelement, the second positioning element, or both.
 2. The method of claim1, wherein the connection flange of the rotor blade comprises at leastone blade stud configured to be inserted into the at least one hubconnection hole, the method further comprising a step of joining asupporting means to the blade in a supporting blade area located betweena maximum chord area and a blade tip, resting the supporting means onthe tower or on at least one tensioned cable when the blade is lifted bymeans of the lifting means and separating the supporting blade area fromthe tower at a distance that, when the first and the second positioningelements cooperate, an axis of the blade stud is substantially parallelto the axis of the hub connection hole.
 3. The method of claim 2,wherein the supporting blade area is located between the maximum chordarea and a center of gravity area.
 4. The method of claim 2, wherein thesupporting means comprises an end contacting the tower surface, andwherein the step of lifting the blade comprises rolling the blade on thetower surface by means of wheels comprised in the end of the supportingmeans contacting the tower surface.
 5. The method of claim 2, furthercomprising a step of adjusting a distance between the blade and thetower by varying dimensions of actuators comprised in the supportingmeans.
 6. The method of claim 2, wherein the step of lifting the bladecomprises sliding, on two tensioned cables, sliding elements comprisedin the supporting means.
 7. The method of claim 1, wherein the step oflifting the blade comprises: attaching a blade raising tool to an outersurface of the blade; and fixing the second positioning element to theraising tool.
 8. The method of claim 7 further comprising attaching, toa cable wherein the second positioning element is fixated, a root-partcomprised in the blade raising tool.
 9. The method of claim 8, furthercomprising the step of fixing, by means of bolts, the blade raising toolto at least three t-bolts of a plurality of t-bolts embedded in the rootarea.
 10. The method of claim 7, wherein the blade raising toolcomprises two halves rotatably connected through a hinge, the methodfurther comprising a step of closing and joining together the two halvesby means of a security attachment element in the form of a hydraulicpiston.
 11. The method of claim 10, wherein the first positioningelement comprises two first positioning elements, wherein the bladeraising tool comprises two second positioning elements which cooperatewith the two first positioning elements attached to a main frame of thenacelle or the tower, and wherein the method further comprises providingeach one of the two second positioning elements in each of the twohalves of the blade raising tool.
 12. The method of claim 1, wherein thelifting means comprise: at least one hoisting system located on theground; at least one cable connected to a blade raising tool by a firstside of the cable and to the hoisting system by a second side of thecable, and a pulley system including at least one pulley detachablyconnected to a component stationary connected with a main frame of thewind turbine or to the tower, wherein the at least one pulley guides theat least one cable from the blade to the hoisting system.